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Comet Hale-Bopp light curve update: best bet is a maximum around -1.0

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Comet Hale-Bopp light curve update: best bet is a maximum around -1.0

Mark Kidger
mrk@ll.iac.es

Recent observations show that the comet is maintaining a steady brightening as it approaches perihelion, with no evidence yet of a slow-down as it reaches 1AU from the Sun. The latest light curve is based on some 650 observations and shows that there has been a significant "jump" in the comet's brightness starting around 50 days before perihelion, which has now flattened out, taking the comet back to virtually the same rate of rise as before. The light curve is now clearly above the line which represents the best fit to the data since October 1996, although almost exactly parallel to it. This shows that Hale-Bopp is still behaving like an "average" dynamically fairly new comet at present, apart from occasional brief outbursts.

Unless something very untoward happens in the next month, the range of maximum magnitude is very unlikely to be outside the range from -0.5 to -1. The observers in the best sites are probably going to estimate a magnitude at maximum which just touches -1.

The absolute magnitude of the comet is now steady at approximately -0.8, the third brightest absolute magnitude recorded since 1400. Comet Sarabat of 1729 (absolute magnitude -3.0) and the Comet of 1577 (-1.8) were intrinsically much brighter, while Comet De Cheseaux of 1747 (not the 6 tailed comet) had an absolute magnitude of -0.5. These three comets and Hale-Bopp are the only ones known to have had an negative absolute magnitude. In fact, with Hale-Bopp, only 10 comets (the last was Comet Humason, in 1962) have had an absolute magnitude brighter than +1.5. This absolute magnitude corresponds to an object which is intrinsically 10 times brighter than Comet Halley.

Observers hoping to see the comet during the total solar eclipse in Mongolia can expect the magnitude to be just slightly brighter than magnitude 0 if the current trend continues.

It is always possible that Comet Hale-Bopp may still surprise us. Comet Hyakutake showed an very marked slow-down on crossing the Earth's orbit and such a slow down might still happen in Hale-Bopp, reducing the maximum brightness a little. Much brighter magnitudes than -1 are also increasingly unlikely as the comet maintains a very steady level of activity with no signs of anything unusual happening. comethome.gif Comet Hale-Bopp Home Page

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